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I stick what looks like a cotton wool bud in my mouth, rub it all over my gums and, being careful not to touch it, I place it into a plastic test tube and seal it with what looks like a silicone earplug. I have just done my first DNA test.

No, I have not been arrested, nor am I trying to solve a paternal identity mystery. I’m just trying to get fitter.

DNA testing is set to be a growing trend in the fitness industry this year. Our genes dictate how we respond to different food and exercise. Knowing which variants you have means you can access the sort of personally tailored training plan that was once only available to elite athletes.

That, at least, is the theory from the company behind it, DNAFit. It started genetic profiling two years ago for Premier League football teams and elite athletes such as 800m runner Jenny Meadows. Then, last year, it worked on a pilot project with NHS Essex to provide overweight patients with DNA tests so they could be given tailored diets based on how their bodies respond to carbohydrates and saturated fats.

Helen's results showed she was not liable to put on weight easily

Now, for £149, we can all have a go. The home testing kit launched in the high street in November. It’s been available to buy online to a niche market of fitness enthusiasts for a year but it’s now gone mainstream due to growing public interest in personal health.

The simple mouth swab - best done in the morning before you brush your teeth – scans 45 gene variants with a proven link to how the body responds to food and exercise. It includes things like sensitivity to carbohydrates, salt and saturated fat; lactose and gluten intolerance risk; individual anti-oxidant and vitamin needs; and caffeine and alcohol metabolism.

Fitness fans can discover if they have a natural aptitude for endurance sports (like running, cycling or swimming) or power sports (like sprinting or weight lifting); their aerobic potential (known as Vo2 max); and how quickly their body is likely to recover between workouts.

Helen was told she had a 65:35 percent bias towards endurance sport compared to power sports

But how accurate are these tests, and will they change anything? As a competitive runner and Team GB age-group triathlete, I was keen to see if my training regime could benefit from some gene-specific tweaking.

My results arrived in two 20-page reports – one for diet, one for fitness. I sought the help of DNAFit’s chief tester Andrew Steele, also an Olympian 400m sprinter, to decipher the results. He got involved with the company five years ago after initially offering his own DNA for research and was so impressed with the results he joined the team.

First, the good news. I’m not likely to put weight on easily. I have a “low” response to saturated fats. Key to this is my variation of the FTO gene - often dubbed the ‘fat gene’.

There are three types: AA, AT and TT. Studies have shown that those with the AA variant are more likely to store body fat when they eat saturated fats. The AT is moderately sensitive to saturated dietary fats. But those blessed with the TT version, like me, have a low sensitivity to dietary fat.

There are some 10 million gene variants in the human body

I can’t relax too much, though as I’m a “medium” responder to carbohydrates. Steele explains: “Some people are more efficient than others at extracting energy from food. A high responder to carbohydrates gets a bigger increase in blood glucose from carbohydrates so they don’t need as much and should be careful not to eat too much. But if you are a low responder you might need more carbohydrates to meet your body’s needs.”

Also, some bad news: I have a raised need for anti-oxidants, omega 3, calcium and several vitamins. I apparently lack the GSTM1 gene, responsible for one stage of detoxification. Andrew advises I eat extra cruciferous vegetables to compensate. I’m impressed. Science has confirmed intuition. I’m an eczema sufferer and I tend to flare up when I don’t have access to fresh fruit and vegetables by the plate-load. My results also show I lack a variant of the LCT gene that enables digestion of dairy products – something else I have noticed triggers my eczema.

More bad news when it comes to alcohol. For some people, a small amount of their favourite tipple can have a positive effect on ‘good cholesterol levels’. But only if you have a certain version of the ADH1C gene. I don’t. So much for that healthy glass of red wine a day.

'It's hard to argue with the results of a DNA test. Or is it?' Credit:
Andrew Brookes/Corbis

That’s the diet report. What about the verdict on my sporting prowess? Well, I’m told I have a 65:35 percent bias towards endurance sport compared to power sports. This means my body will have a greater response to longer aerobic training than it would to short bursts of powerful exercise like sprinting. So far so good, since triathlon is an endurance sport.

I have a ‘high’ aerobic potential, which means that with training I’m likely to achieve a high VO2 max (the rate at which our bodies process oxygen and which enables us to sustain aerobic activity). But I’m not happy to discover my likelihood for developing soft tissue injury is ‘high’ and my ‘recovery speed’ is below average. This means, according to Steele, I should allow 48 hours for my nervous system to recover between high intensity workouts, such as my weekly track running session or hill sprints. ‘Fast’ recoverers can get away with 24 hours.

In January, the market for new diet and fitness plans is saturated, but it's hard to argue with the results of a DNA test. Or is it? Some experts are skeptical. There are some 10 million gene variants in the human body (referred to as SNPs). The DNAFit test only looks at 45 of them – those which have passed three scientifically validated studies. This, says Mark Thomas, professor of evolutionary genetics at University College London, means the test gives us only a small window into our genetic profile.

‘Fast’ recoverers can get away with 24 hours between each high intensity workoutCredit:
JOHNER IMAGES / ALAMY

“We’ve only just scratched the surface with genetics,” he says. “There are performance differences that are genetically determined and there will be a point when we know more, but now, these tests are only weakly informative. If you want to know how good someone is likely to be at sport, you’ll probably get a better idea by looking at them and their body shape.”

Could it, moreover, be counterproductive to know too much about our diet genes? Say someone is told they have the AA version of the ‘fat gene’ (the one sensitive to dietary fats), or that they have low ‘aerobic potential’, might they just give up trying to get fit?

Steele thinks not. “There are no good or bad genes. People’s perspective on genetics is that everything is pre-determined. But genetic testing is about enabling you to manipulate your environment based on how your body works. It allows us to make a personalised training or nutritional plan, rather than a one size fits all.”

As for me, while I found it fascinating to get a personalised reading of how my body works, much of it I already knew instinctively.

I knew, for instance, that I found endurance training easier than speed training. I had already worked out that eating dairy didn’t suit me and that I needed lots of vegetables to keep my digestive system happy, so those results weren’t surprising. But having scientific validation of my own DIY health approach was satisfying.

There is one other concern with genetic fitness tests, however: if they do go mainstream, where will it lead? Will we have ‘genetic type’ gym classes or geno-type food labeling? What about competitive sport? Instead of being segregated by sex or weight, will athletes be segregated based on genetic advantage? Maybe it’s best we don’t know our limitations.